A chlorinated polyolefin is prepared by chlorinating a polyolefin in the form of solution or suspension in a solvent. Such a chlorinated polyolefin molecule contains 10 to 80% by weight of chlorine. The chlorinated polyolefin is used in vulcanized or unvulcanized form. Because of its excellent fire retardance, weathering resistance, ozone resistance, chemical resistance and electrical characteristics, the chlorinated polyolefin is utilized as a modifier for resin such as polyvinyl chloride, bright electric wire, bright sponge, etc.
On the other hand, a chlosulfonated polyolefin is prepared by chlorosulfonating a polyolefin in the form of solution or suspension in a solvent. Such a chlorosulfonated polyolefin molecule contains 20 to 60% by weight of chlorine and 0.3 to 3.0% by weight of sulfur. The chlorosulfonated polyolefin can be easily vulcanized in the presence of a metallic oxide and vulcanization accelerator to prepare an elastomer having excellent weathering resistance, ozone resistance, heat resistance, chemical resistance and brightness.
However, one of the disadvantages of a chlorinated polyolefin and chlorosulfonated polyolefin is poor cold resistance.
With reference to the chlorosulfonated polyolefin, JP-A-60-144306 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") proposes a process for the preparation of a chlorosulfonated polyolefin having excellent low temperature characteristics by using an aromatic compound as a solvent for the purpose of overcoming the foregoing difficulty. However, a chlorosulfonated polyolefin prepared by using an aromatic compound as a solvent is disadvantageous in that it can be easily colored during heat aging.
On the other hand, the solution which has undergone the chlorination or chlorosulfonation reaction contains hydrogen chloride gas and/or sulfur dioxide gas by-produced during the reaction. These hydrogen chloride and sulfur dioxide gases are corrosive materials. Therefore, it is not preferable from the standpoint of preparation that the chlorinated polyolefin or chlorosulfonated polyolefin is isolated from the solution containing these corrosive materials. Accordingly, these corrosive materials are excluded from the reaction system before the isolation of chlorinated polyolefin or chlorosulfonated polyolefin. Heretofore, in order to exclude hydrogen chloride gas and/or sulfur dioxide gas by-produced during the reaction from the reaction system, an approach has been employed which comprises blowing nitrogen through the reaction system at the boiling point of the solvent used. However, this approach is disadvantageous in the case where a high boiling solvent (e.g., solvent having a boiling point of 100.degree. C. or higher) is used to prepare a chlorinated polyolefin or chlorosulfonated polyolefin in that if hydrogen chloride and/or sulfur dioxide by-produced at the boiling point of the solvent used is excluded from the reaction system, a colored chlorinated polyolefin or chlorosulfonated polyolefin is obtained.
The foregoing problem of coloring drastically impairs the desired brightness of the chlorinated polyolefin or chlorosulfonated polyolefin. It has thus been desired to solve this problem.